October 18, 2019
Texas A&M University
Mars once had salt lakes that
are similar to those on Earth and has gone through wet and dry periods.
Mars once had salt lakes that
are similar to those on Earth and has gone through wet and dry periods,
according to an international team of scientists that includes a Texas A&M
University College of Geosciences researcher.
Marion Nachon, a postdoctoral
research associate in the Department of Geology and Geophysics at Texas
A&M, and colleagues have had their work published in the current issue
of Nature Geoscience.
The team examined Mars'
geological terrains from Gale Crater, an immense 95-mile-wide rocky basin that
is being explored with the NASA Curiosity rover since 2012 as part of the MSL
(Mars Science Laboratory) mission.
The results show that the lake
that was present in Gale Crater over 3 billion years ago underwent a drying
episode, potentially linked to the global drying of Mars.
Gale Crater formed about 3.6
billion years ago when a meteor hit Mars and created its large impact crater.
"Since then, its
geological terrains have recorded the history of Mars, and studies have shown
Gale Crater reveals signs that liquid water was present over its history, which
is a key ingredient of microbial life as we know it," Nachon said.
"During these drying periods, salt ponds eventually formed. It is
difficult to say exactly how large these ponds were, but the lake in Gale
Crater was present for long periods of time -- from at least hundreds of years
to perhaps tens of thousands of years," Nachon said.
So what happened to these salt
lakes?
Nachon said that Mars probably
became dryer over time, and the planet lost its planetary magnetic field, which
left the atmosphere exposed to be stripped by solar wind and radiation over
millions of years.
"With an atmosphere
becoming thinner, the pressure at the surface became lesser, and the conditions
for liquid water to be stable at the surface were not fulfilled anymore,"
Nachon said. "So liquid water became unsustainable and evaporated."
The salt ponds on Mars are
believed to be similar to some found on Earth, especially those in a region
called Altiplano, which is near the Bolivia-Peru border.
Nachon said the Altiplano is
an arid, high-altitude plateau where rivers and streams from mountain ranges
"do not flow to the sea but lead to closed basins, similar to what used to
happen at Gale Crater on Mars," she said. "This hydrology creates
lakes with water levels heavily influenced by climate. During the arid periods
Altiplano lakes become shallow due to evaporation, and some even dry up
entirely. The fact that the Atliplano is mostly vegetation free makes the
region look even more like Mars," she said."
Nachon added that the study
shows that the ancient lake in Gale Crater underwent at least one episode of
drying before "recovering." It's also possible that the lake was
segmented into separate ponds, where some of the ponds could have undergone
more evaporation.
Because up to now only one
location along the rover's path shows such a drying history, Nachon said it
might give clues about how many drying episodes the lake underwent before
Mars's climate became as dry as it is currently.
"It could indicate that
Mars's climate 'dried out' over the long term, on a way that still allowed for
the cyclical presence of a lake," Nachon said. "These results
indicate a past Mars climate that fluctuated between wetter and drier periods.
They also tell us about the types of chemical elements (in this case sulphur, a
key ingredient for life) that were available in the liquid water present at the
surface at the time, and about the type of environmental fluctuations Mars life
would have had to cope with, if it ever existed."
Story Source:
Materials provided by Texas A&M University.
Original written by Keith Randall. Note: Content may be edited for style
and length.
Journal Reference:
W. Rapin, B. L. Ehlmann, G.
Dromart, J. Schieber, N. H. Thomas, W. W. Fischer, V. K. Fox, N. T. Stein, M.
Nachon, B. C. Clark, L. C. Kah, L. Thompson, H. A. Meyer, T. S. J. Gabriel, C.
Hardgrove, N. Mangold, F. Rivera-Hernandez, R. C. Wiens, A. R. Vasavada. An
interval of high salinity in ancient Gale crater lake on Mars. Nature
Geoscience, 2019; DOI: 10.1038/s41561-019-0458-8
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